The present invention relates to the field of valve lifter constructions for internal combustion engine, and in particular to a mechanical type of valve lifter construction which can be used with an internal combustion engine which can also easily be adapted to utilize a hydraulic type of valve lifter construction.
In the prior art there are several known types of valve lifter construction for internal combustion engines. There is the mechanical type of valve lifter construction, in which a cam bears on valve lifter member which in turn pushes on a push rod, and in which excess play (so called lash adjustment) is taken up by mechanical adjustment as by the adjustment of a tappet screw fitted with a lock nut--and this type, which incorporates no system component utilizing oil pressure, is too well known to require illustration or further description herein. Alternatively, there is an oil pressure type of hydraulic valve lifter construction, which performs lash adjustment to a zero lash condition by supply of pressurized lubricating oil to an oil compartment thereof, to expand the size of said oil compartment. Such a type of per se conventional valve lifter construction is shown in FIG. 4 of the accompanying drawings in longitudinal cross section. This valve lifter construction, designated as 25 in the figure, is of the type shown and described in Japanese Utility Model Laying Open Publication Serial No. 57-160905 (1982). It comprises an outer casing 26 formed in the shape of a cylinder with a closed end or a cup shape, a lifter bore 12 within which said outer casing 26 reciprocates, a cam shaft 15 with a cam 16 for actuating said outer casing to reciprocate it, a plunger portion 27 and a plunger cap 28 which are fitted in the inside of said outer casing 26, a check valve ball 29, a check valve spring 30, and a plunger spring 31. The outer casing 26 is provided with a lubricating oil intake port 33 which, as said outer casing 26 reciprocates in said lifter bore 12, repeatedly comes into register with an opening 19a where a lubricating oil passageway 19 formed through the engine cylinder block assembly opens into said lifter bore 12 at an axially intermediate position therealong. The passageway 19 is continually supplied with lubricating oil at a high pressure value, and accordingly, every time the intake port 33 comes into register with the opening 19a, pressurized lubricating oil is admitted into an oil chamber 32 located within the valve lifter, thus to increase the length of the valve lifter construction as much as possible. This means that all excess play in the valve train is taken up by such increase of the length of the valve lifter construction; if further details of the operation of this hydraulic type valve lifter construction are required, reference should be made to the above identified Japanese Utility Model Laying Open Publication Serial No. 57-160905 (1982).
On the other hand, the valve lifter portion of a mechanical type valve lifter construction is typically formed in a cup shape, that is, as a hollow cylinder with a closed bottom and a cylindrical side wall portion rising therefrom to define an open top, with the lower or outer side of the closed bottom riding on the cam and with the lower end of the push rod seated against the upper or inner side of said closed bottom with said push rod protruding upwards out of said open end, and it is usual to form one or two radially extending holes through the cylindrical side wall portion of said valve lifter, for allowing oil that has flowed into the interior of the cup shape thereof to escape and to lubricate the contact portion between said outer side of said closed bottom and said cam. This oil escape hole is essential for thus supplying lubrication to said contact portion. Further, during the process of manufacture of such valve lifters, which is typically done by casting a plurality of them together, these radial holes are naturally defined by the matrix portion of the core for casting. Thus, in summary, such oil escape holes cannot be omitted from a mechanical valve lifter construction.
Now, in order to avoid the undue proliferation of different types of engine parts, and in view of the fact that it is desirable to be able to offer to the public both engines which utilize mechanical type valve lifter constructions and also engines which utilize hydraulic type valve lifter constructions, it would be very desirable, even in the case of utilization of a mechanical type valve lifter construction, for the same engine cylinder block assembly to be used, as was used in the case of a hydraulic type valve lifter construction. In other words, it would be desirable for only one type of cylinder block assembly to be fittable either with mechanical type valve lifter constructions or with hydraulic type valve lifter constructions, as required. This would mean that only one type of cylinder block assembly would need to be manufactured for both such types of engine, and the consequent advantages in terms of production convenience and also stocking economy are manifest.
The difficulty engendered by this, however, is as follows. As the mechanical valve lifter of the type outlined above moves up and down in a valve lifter bore adapted for use with a hydraulic type valve lifter, such as the bore 12 of the FIG. 4 construction in which pressurized oil is being supplied to a side opening such as the opening 19a at an axially intermediate position therealong, when the aforementioned radial oil escape hole comes into register with the side opening, then a considerable volume of oil will inevitably spurt from said side opening into the cup space within the valve lifter. And this creates the danger of a sharp drop in lubricating oil pressure in the lubricating system for the engine, which could be very troublesome.